US Patent 7234357 Wafer bonded pressure sensor

A pressure sensor (30) for sensing a fluid pressure in harsh environments such as the air pressure in a tire, by using a first wafer substrate (32) with a front side and an opposing back side, a chamber (58) partially defined by a flexible membrane (50) formed on the front side and at least one hole (33) etched from the back side to the chamber (58);a second wafer (31) on the back side of the first wafer (32) to seal the at least one hole (33); wherein,the chamber (58) containing a fluid at a reference pressure, such that the flexible membrane (50) deflects due to pressure differentials between the reference pressure and the fluid pressure; and,associated circuitry (34) for converting the deflection of the flexible membrane (50) into an output signal indicative of the fluid pressure; wherein,the second wafer (31) is wafer bonded to the first wafer substrate (32).